CS 240 – Advanced Programming Concepts Logging CS 240 – Advanced Programming Concepts

Java Logging Java has built-in support for logging Logs contain messages that provide information to Software developers (e.g., debugging) System administrators Customer support agents Programs send log messages to “loggers” There can be one or more Each message has a “level” SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST

Java Logging Loggers have a method for each message level that are used to enter messages in the log severe, warning, info, config, fine, finer, finest Rather than removing debugging log messages from the code, we leave them in Loggers can be configured to include or omit log messages based on their levels Logger.setLevel(level) method ALL (include all messages) OFF (omit all messages) SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST (include all messages at a particular level and higher)

Java Logging Each logger has one or more “handlers” associated with it Handlers represent destinations to which the log messages should be sent ConsoleHandler (sends messages to the console) FileHandler (sends messages to a file) SocketHandler (sends messages to a network socket) Like loggers, handlers can also be configured to include or omit log messages based on their levels Handler.setLevel(level) method ALL (include all messages) OFF (omit all messages) SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST (include all messages at a particular level and higher)

Java Logging Each handler has a “formatter” which defines the format used to encode its messages SimpleFormatter XMLFormatter

Programmatic Configuration public class ProgrammaticConfigurationExample { private static Logger logger; static { try { initLog(); } catch (IOException e) { System.out.println("Could not initialize log: " + e.getMessage()); } } private static void initLog() throws IOException { Level logLevel = Level.FINEST; logger = Logger.getLogger("ProgrammaticConfigurationExample"); logger.setLevel(logLevel); logger.setUseParentHandlers(false); Handler consoleHandler = new ConsoleHandler(); consoleHandler.setLevel(logLevel); // consoleHandler.setFormatter(new SimpleFormatter()); logger.addHandler(consoleHandler); FileHandler fileHandler = new FileHandler("log.txt", false); fileHandler.setLevel(logLevel); // fileHandler.setFormatter(new SimpleFormatter()); logger.addHandler(fileHandler); }

File Configuration Example import java.util.logging.Level; import java.util.logging.Logger; /** * Specify the configuration file by adding the following VM option * in the run configuration or you will get the default logging * configuration: * * -Djava.util.logging.config.file=logging.properties * */ public class FileConfigurationExample { private static Logger logger = Logger.getLogger("FileConfigurationExample"); }

Logging Configuration File handlers=java.util.logging.FileHandler, java.util.logging.ConsoleHandler java.util.logging.ConsoleHandler.level=FINE java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter java.util.logging.FileHandler.level=FINE java.util.logging.FileHandler.pattern=log.txt # Write 10MB before rotating this file java.util.logging.FileHandler.limit=10000000 # Number of rotating files to be used java.util.logging.FileHandler.count=4 java.util.logging.FileHandler.formatter=java.util.logging.SimpleFormatter # Log format to use java.util.logging.SimpleFormatter.format=%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS %4$s %2$s %5$s%6$s%n .level=FINEST

Log Formatting Use format specifiers from the java.util.Formatter class Available variables to log: %1$ The date/time the message was created %2$ The method that called the log method %3$ The name of the logger %4$ The level the message was logged at %5$ The message %6$ The throwable

Logging Messages Logging messages with specific levels severe(message) Same for warning, info, config, fine, finer, finest log(level, message) Logging method enter/exit entering(className, methodName) exiting(className, methodName) Logged at FINER level Logging throwing an exception throwing(className, methodName, throwable) Logging catching an exception log(level, message, throwable)

Logging Message import java.util.logging.Level; import java.util.logging.Logger; /** * Specify the configuration file by adding the following VM option in the run configuration * or you will get the default logging configuration: * * -Djava.util.logging.config.file=logging.properties * */ public class FileConfigurationExample { private static Logger logger = Logger.getLogger("FileConfigurationExample"); public static void main(String [] args) { logger.info("This is my info log message."); logger.fine("This is my fine log message"); try { throw new Exception("An exception occurred"); } catch (Exception ex) { logger.severe("This is my exception message"); logger.log(Level.SEVERE, "This is my message logged with the exception", ex); } } }

Logging Messages import java.util.logging.*; public class Server { private static Logger logger = Logger.getLogger(”Server"); private void run() { logger.info("Initializing HTTP Server"); try { server = HttpServer.create(new InetSocketAddress(SERVER_PORT_NUMBER), MAX_WAITING_CONNECTIONS); } catch (IOException e) { logger.log(Level.SEVERE, e.getMessage(), e); return; } logger.info("Creating contexts"); server.createContext("/games/list", new ListGamesHandler()); server.createContext("/routes/claim", new ClaimRouteHandler()); logger.info("Starting HTTP Server"); server.start();

Logging Messages class ClaimRouteHandler implements HttpHandler { private static Logger = Logger.getLogger("ClaimRouteHandler"); @Override public void handle(HttpExchange exchange) throws IOException { logger.entering("ClaimRouteHandler", "handle"); try { ... logger.fine(reqData); } catch (IOException e) { logger.log(Level.SEVERE, e.getMessage(), e); logger.exiting("ClaimRouteHandler", "handle");

Log4J Java didn’t have a logging API until version 1.4 Before 1.4, we had to log with System.out.println(…) or System.err.println(…) Or, use an external framework Log4J became very popular and widely used before 1.4 Log4J is still more commonly used than the built-in java.util.logging API Log4J is very similar to java.util.logging